Mold insert

ABSTRACT

A substantial barrier to flow of liquid in a circumferentially-extending liquid conduit groove of a mold insert is provided by forming recesses or undercuts by undercutting the sidewalls of the liquid conduit groove, inserting a plate-like liquid dam within the liquid conduit groove, and clamping the dam in the liquid conduit groove by the use of a pair of locking screws or pins that extend through bores in the dam into engagement with inwardly-facing surfaces of the undercuts. The relationship between the inwardly-facing undercut surfaces and the locking members is preferably such that there is a progressively increasing interfering engagement of the locking members with the undercut surfaces resulting in increasing clamping pressures applied to the dam assemblies.

This is a divisional of application Ser. No. 08/296,096, filed on Aug.25, 1994, abandoned, which is a continuation of application Ser. No.07/966,813, filed on Oct. 26, 1992, abandoned. This is also related toapplication no. 08/387,250, filed Feb. 13, 1995, now Pat. No. 5,647,114,and to application No. 08/392,062, filed Feb. 22, 1995.

BACKGROUND OF THE INVENTION

This invention relates to an improved mold insert. Mold inserts of thetype to which this invention pertains are used in machines for injectionmolding plastic workpieces, but this invention may be useful in otherfields, such as die casting and rubber molding.

This invention is disclosed for use with mold inserts of the type shownin my U.S. Pat. No. 4,828,479, granted May 9, 1989, and U.S. Pat. No.4,959,002, granted Sep. 25, 1990, the disclosures of which are herebyincorporated by reference herein. (The '479 and the '002 patents arehereinafter referred to as “said patents”.) Said patents disclosegenerally cylindrical mold inserts for injection mold machines whichhave a generally cylindrical liquid channel section with a liquidconduit groove extending circumferentially around the liquid channelsection. A liquid barrier is located in the groove so that the groove isdouble-ended, one end constituting a liquid inlet end and the other endconstituting a liquid outlet end. A mold machine with which an insert isused has inlet and outlet connectors aligned with the inlet and theoutlet ends of the groove so that a liquid, which is usually water, canbe circulated around the insert for cooling or heating portions of theinsert.

The mold inserts to which said patents relate are used in matched pairs,one being mounted on an “A” plate of an injection molding machine andthe other mounted on its confronting “B” plate. Proper orientation ofinserts on their respective “A” and “B” plates is maintained byinterfitting keys and notches. The liquid inlets and outlets for boththe “A” and the “B” plates are usually located on the same side of amaster frame. If one were able to look at the liquid barriers of a pairof mutually confronting inserts from the outside of a master frame, bothliquid barriers would appear to be on the same side of the master frame.However, one looking at the “A” plate insert from its front face wouldobserve that its liquid barrier is on one side of the insert and, uponlooking at the “B” plate insert from its front face, would observe thatits liquid barrier is on the opposite side. Thus, for example, if theliquid barrier of the “A” plate insert is located at the 3:00 o'clockposition, as viewed from the front face of the insert, then the liquidbarrier on the “B” plate insert would be at the 9:00 o'clock position,as viewed from its front face.

Until machined to form the shapes of the mold cavities and cores, theonly difference between an insert usable with an “A” plate of a moldmachine and one usable with a “B” plate for the same machine is inregard to the location of the inlet and outlet barrier. This differencecreates an inventory problem for a supplier of inserts. The practice hasbeen to inventory inserts without the barriers and to weld dams thatform the barriers into the liquid grooves when the inserts are removedfrom inventory for use or sale. The welding operations must be carriedout with care, not only to insure that each dam is installed in theproper location, but also to insure that a dam will not, during use,slide or otherwise move around in the liquid conduit groove and will notwork loose while the insert cavity or core is being machined. (Themachining operations are usually done, at least in part, on turninglathes which rotate the inserts at high speeds and there is a dangerthat a loose dam would fly away from a rotating insert and cause injuryto the lathe operator.) The use of the described welding procedure isobviously inefficient and costly because it requires the availability ofa skilled welder when each insert is removed from inventory in order toinsure that a liquid barrier is properly formed. Of course, an optionwould be to inventory inserts having inlet and outlet barriers alreadyformed. However, that would require twice the inventory to reasonablyinsure that there would be an adequate supply of inserts usable with “A”plates and also an adequate supply of inserts usable with “B” plates.

The user of a mold insert often drills liquid passageways extendinginwardly from circumferentially-extending liquid conduit grooves to meetvarious cooling or heating needs. To insure an adequate flow of liquidinto such inwardly directed passageways, one or more additional dams orbarriers are affixed inside the peripheral liquid conduit groove. Theprovision of additional dams or barriers, using the present weldingprocedures, can be time consuming and costly.

Accordingly, there exists a need to improve the efficiency with whichinserts can be inventoried and there is also a need to enable the userof an insert to quickly, accurately and securely assemble liquid dams orbarriers into liquid conduit grooves of mold inserts.

SUMMARY OF THE INVENTION

An object of this invention is to provide an improved mold insert formolding machines, and a liquid dam or barrier assembly therefor, whichwill enable the liquid dam or barrier assembly to be easily, quickly,accurately, and securely installed without the use of special tools ormachines, such as welders, into liquid conduit grooves extendingperipherally around the mold insert.

Another object of this invention is to provide improved dam or barrierassemblies for use with mold inserts. More particularly, an object ofthis invention is to provide a self-contained dam assembly whichincludes means for clamping a dam body member to the inside surfaces ofa liquid conduit groove in a mold insert utilizing locking members, suchas screws or pins, moveable in bores in the dam body member which opento the outermost surfaces of the dam body member, the clamping of thedam assembly to the surfaces of the liquid conduit groove beingaccomplished by engaging the exposed heads of the locking members by asimple tool.

In accordance with this invention, a substantial barrier to the flow ofliquid in a circumferentially-extending liquid conduit groove of a moldinsert is provided by forming recesses or undercuts by undercutting thesidewalls of the liquid conduit groove, inserting a plate-like liquiddam body member within the liquid conduit groove, and clamping the dambody member in the liquid conduit groove by the use of locking membersthat extend through bores in the dam body member into engagement withinwardly-facing surfaces of the undercuts. The relationship between theinwardly-facing undercut surfaces and the locking members is preferablysuch that, during assembly, there is a progressively increasinginterfering engagement of the locking members with the undercut surfacesresulting in increasing clamping pressures being applied to the damassemblies.

More particularly, the bores in the dam body member extend therethroughin opposite directions from its top surface downwardly and outwardlytoward its opposite sides. When assembled into a liquid conduit groove,the top surface of the dam body member becomes its radially outermostsurface with respect to the longitudinal centerline of the insert. Thedam is so sized and shaped that it fits entirely within the liquidconduit groove and is effective to substantially prevent the flow ofliquid therepast. One such dam can be clamped within a liquid conduitgroove to separate or define the liquid inlet and outlet ends thereof.One or more additional dams can readily be clamped within the liquidconduit groove to assist in forcing the liquid into passagewaysextending from the liquid conduit groove.

The undercuts in the sidewalls of the liquid conduit groove preferablyextend completely through 360 degrees to enable them to be easilymachined using a turning lathe and to enable the user to easily add damassemblies at any desired location around the periphery of the liquidconduit groove. Each undercut preferably has sloping outermost surfacesthat face inwardly toward the base surface of the liquid conduit grooveat an angle relative to the base surface which is greater than theangles of the axes of the locking members relative to said base surfacewhen a dam assembly is installed. Accordingly, when the locking membersare driven into engagement with the inwardly facing undercut surfaces,the leading ends of the clamping members engage and tend to gouge intothe undercut surfaces. In addition, the undercuts and the dam bodymembers are preferably so formed that the locking members engage onlythe sloping outermost surfaces of the undercuts. The advancement of thelocking members against the inwardly-facing undercut surfaces of theundercuts is restricted only by the interference between the lockingmembers and the inwardly-facing undercut surfaces, the parts being soformed that the locking members never engage other surfaces of theliquid conduit groove or its undercuts.

In the presently preferred embodiment of this invention the bores in thedam body members are tapped and the locking members comprise shortlocking screws threadedly mounted within the tapped bores. The screwsare provided with heads designed to interfit with a simple tool so thatthe screws can easily be advanced by rotation into interferingengagement with the inwardly-facing undercut surfaces. Substantialfrictional forces are generated between the screws and theinwardly-facing undercut surfaces causing the screw threads to be bentor flattened and the undercut surfaces to be roughened so that thelocking screws remain tightly engaged with the undercut surfaces and thedam assembly is securely and tightly clamped in place. The use oflocking screws is preferred because they are strong and reliable yetinexpensive and simple to use. Moreover, the locking screws can readilybe removed, by reverse rotation, from engagement with the undercutsurfaces to enable one readily to reposition or remove and replace damassemblies.

In a modification, the locking members comprise short locking pins whichare driven by force through the dam member bores, which may be smoothand not tapped, into interfering engagement with the inwardly-facingundercut surfaces. These locking pins can readily be driven by a punch.Locking pins can also be strong, reliable, inexpensive and relativelyeasy to use. A drawback to their use is that dam assemblies usingunthreaded pins or the like are not easily repositioned or removed.However, there may be applications in which such pins would bepreferred.

Other objects and advantages will become apparent from the followingdescription and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a partly assembled mold insert made inaccordance with this invention.

FIG. 2 is a fragmentary, exploded perspective view of the mold insertbody of FIG. 1 and a liquid dam assembly in accordance with thisinvention.

FIG. 3 is a fragmentary cross-sectional view of the mold insert of FIG.2 with the dam assembly clamped to the insert body.

FIG. 4 is a top plan view of the dam assembly of FIGS. 2 and 3. FIG. 4and the figures that follow are on a larger scale than FIGS. 1 through3.

FIG. 5 is a view partly in cross section and partly in elevation of thedam assembly indicated generally by view line 5—5 of FIG. 4.

FIG. 6 is a fragmentary cross-sectional view of a portion of the moldinsert body.

FIG. 7 is a fragmentary cross-sectional view of the same portion of themold insert body illustrated in FIG. 6 and a dam assembly clampedtherein.

FIG. 8 is a fragmentary cross-sectional view of a portion of a moldinsert body and a modified dam assembly in accordance with thisinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the drawings, a mold insert in accordance with thisinvention is generally designated 10 and comprises an insert body,generally designated 12, and one or more dam assemblies, generallydesignated 14. Pairs of inserts 10 are mounted in mutually confrontingrelation in the “A” and “B” plates (not shown) of a master frame (notshown). As explained in said patents, the mold insert 10 may compriseeither a cavity insert or a core insert. (It should be understood thatthe reference numbers used herein are not the same as the referencenumbers applied to corresponding parts in said patents.)

Insert body 12 comprises a solid, one-piece metal body which is steppedalong its length to comprise three disc-shaped, longitudinally-adjacentsections, namely a first, largest diameter, locking section, generallydesignated 16, a second, intermediate diameter, liquid channel section,generally designated 18, and a third, smallest diameter base section 20.As described in greater detail in said patents, the locking groovesection 16 has a pair of mutually diametrically-opposed flats 22 and apair of locking grooves 24 that extend, respectively, circumferentiallybetween the tops of the flat 22 and the bottoms of the flats 22. (Onlythe upper groove 24, which extends from the top of one flat 22 to thetop of the other flat 22 is shown in the drawings.) Locking groovesection 16 further has a rear face or shoulder 28 that bears against acooperating shoulder (not shown) in its associated “A” or “B” plate. Asfurther described in said patents, the locking grooves 24 are used withretainer and lifter assemblies (not shown) which are used in theassembly and disassembly of the insert 10 with respect to its associated“A” or “B” plate. Proper orientation of the insert 10 within itsassociated plate is maintained by a pair of keys (not shown) thatcooperate with the flats 22 and another key (not shown) that projectsinto a notch 30 in the outer edge of the locking section 16.

The intermediate diameter or liquid channel section 18 has a circularouter surface 32 straddled by grooves 31 and 33 used to receive O-rings(not shown) that seal the liquid channel section 16 when the insert isassembled into an “A” or a “B” plate. The circular outer surface 32 isof uniform diameter except for a peripherally-extending liquid conduitgroove 34. In said patents, the liquid conduit groove is described asextending approximately 340 degrees around the periphery of the liquidchannel section with the ends of the groove spaced by a barrier section.In actual practice, the groove is initially formed to extend 360 degreesaround the periphery of the liquid channel section and, thereafter, thebarrier is formed by welding a plate-like dam piece into the 360 degreegroove.

In accordance with the present invention, the liquid conduit groove 34is also initially formed to extend 360 degrees around the periphery ofthe liquid channel section 18. As best shown in FIG. 6, the liquidconduit groove 34 has a pair of sidewalls 36 and a radially innermost orbottom wall or surface 38. Circumferentially-extending recesses orundercuts 40 having sloping, radially-outermost, inwardly-facing,surfaces 42 are formed in the sidewalls 36 by undercutting the sidewalls36 contiguous to the bottom wall 38 along their entire length. Forreasons which will be discussed, the radially outermost surfaces 42 ofthe recesses 40 slope at an angle “a” which is greater than 45 degreesrelative to the groove bottom wall 38. An angle “a” of approximately 55degrees is acceptable.

With reference to FIGS. 3, 4, 5 and 7, each dam assembly 14 comprises aplate-like body member, generally designated 50, in the form of arectangular parallelepiped having a top wall 52, a bottom wall 54, leftand right sidewalls 56 and 58, respectively, and oppositely-directed endwalls 60 and 62. A pair of threaded or tapped bores 64 extendintermediate and parallel to the ends walls 60 and 62 completely throughthe body member 50 in respectively opposite directions, downwardly andoutwardly from its top wall or surface 52 to the intersection betweenits bottom wall or surface 54 and its respective left and rightsidewalls 56 and 58.

Located within each of the tapped bores 64 are locking screws 66 whichare sufficiently short that they do not project beyond the upper surface52 of the dam body member 50. Locking screws 66 have Allen heads or someother shape suitable so that a simple screw driver or wrench can be usedto drive the locking screws 66 by rotation into the bores 64. Asillustrated in FIGS. 5 and 7, the axes of the bores 64 and, accordingly,the axes of the locking screws 66, extend at an angle “b” relative tothe bottom surface 54 of dam body member 50 which is somewhat less thanthe angle “a”, and is preferably 45 degrees.

As is evident from the drawings, the width of the dam body member 50 issubstantially equal to the width of the liquid conduit groove 34 betweenits mutually confronting sidewalls 36. Likewise, the thickness of thebody member 50, that is, the height of its sidewalls 56 and 58, issubstantially equal to the depth of the groove 34. When a dam assembly14 is clamped within the liquid conduit groove 34, the locking screws 66are located entirely within the liquid conduit groove 34 and the dambody member 50. Accordingly, the dam assembly 14 substantiallycompletely fills the area of the section of the groove 34 in which it islocated and no part of the dam assembly 14 projects radially outwardlyof the groove 34 beyond the circular outer surface 32. It may be notedthat the dam body member 50, being preferably flat and in the form of arectangular parallelepiped, will not entirely fill the section of thegroove 34 and its undercuts 40 in which the dam assembly 14 is located.The locking screws 66, because they project partly into the undercuts40, provide some additional barrier to water flow, but it is apparentthat the barrier to water flow provided by a dam assembly 14 will not beperfect. However, the barrier is sufficiently complete for practicaluse. Of course, it is apparent that dam body members could be made toshapes other than rectangular parallelepipeds provided that the shapesare such as to substantially fill a section of the groove 34 and itsundercuts 40.

In use, as shown best in FIGS. 3 and 7, a dam assembly 14 is placedwithin the liquid conduit groove 34 with its bottom surface 54 engagedwith the groove base surface 38. When so positioned, the dam assembly 14is located completely within the margins of the groove 34, substantiallyfilling or spanning the entire cross-sectional area thereof. The axes ofthe locking screws 66 are located sufficiently close to the outermostsurfaces 42 of the undercuts 40 that the locking screws 66 may be drivenby rotation into engagement with such sloping outermost surfaces 42.Because the angle “b” is smaller than the angle “a”, the locking screws66 are progressively driven further into an interfering engagement withthe sloping outermost undercut surfaces 42 as the locking screws 66 aredriven further into the bores 64. The dam body member 50 is, therefore,effectively wedged with progressively increasing clamping forces againstthe bottom surface 38 of the groove 34. Thus, the dam assembly 14 issecurely locked in the liquid conduit groove 34 so that it will notslide about or work loose.

The interference between the locking screws 66 and the inwardly-facingundercut surfaces 42 causes the threads on the locking screws 66 to bebent or flattened and the undercut surfaces 42 to be mutilated orroughened. As a result, the locking screws 66 tend to remain tightlyengaged with the undercut surfaces 42. The combined actions of theclamping forces described above applied to the dam body member 50 andthe frictional forces between the interengaged locking screws 66 andundercut surfaces 42 cause the dam assembly 14 be reliably, securely andtightly clamped within the liquid conduit groove 34.

An advantage of the dam assembly 14 is that, although retraction of thelocking screws 66 from the undercut surfaces 42 is frictionallyresisted, the locking screws 66 can be retracted by rotation, again withthe use of a suitable tool, to permit removal of the dam assembly 14.This offers the advantage that one may reposition a dam assembly 14,should that be desired, or one may remove and replace a dam assembly 14.As is evident, it would be easier and quicker to remove or replace thedam assemblies 14 of this invention than to remove or replace welded damassemblies.

As shown best in FIG. 7, the bores 64 are so located relative to thebottom wall 38 of the groove 34 that the locking screws 66 are spacedoutwardly from the bottom wall 38 when the locking screws 66 are fullyengaged with the inwardly-facing undercut surfaces 42. Accordingly, theadvancement of the locking screws 66 against the inwardly-facingundercut surfaces 42 is unrestricted by other surfaces of the liquidconduit groove 34 or its undercuts 40.

FIG. 1 illustrates a dam assembly 14 fitted in the liquid conduit groove34 used to provide a barrier for separating and defining the liquidinlet and outlet ends of the groove 34. FIG. 1 further illustrates apair of liquid passageways 70 that extend into the insert body 12. Asillustrated in FIG. 2, the passageways 70 are joined together inside theinsert body 12 and their openings to the liquid conduit groove 34 areseparated by another dam assembly 14 to insure that liquid flowingwithin the groove 34 will by diverted into and through the passageways70.

FIG. 8 shows a modified dam assembly 14A having a dam body member 50Aprovided with smooth-walled (untapped) bores 64A used to provide aliquid barrier in a liquid conduit groove 34 of an insert body 12. Theinsert body 12 of FIG. 8 may be identical to the insert body 12described above and illustrated in FIGS. 1, 2, 3, 6 and 7, and likeparts thereof are referred to by like reference numbers. Instead ofusing the locking screws 66 of the previously described embodiment, themodification of FIG. 8 uses locking members in the form of locking pins66A which are unthreaded and which are snugly or tightly received withinthe bores 64A. Locking pins 66A may be generally cylindrical, asillustrated in FIG. 8, but could have other cross sections, for examplerectangular or hexagonal, and their outer surfaces could be roughened asby knurling.

The dam body member 50A of FIG. 8 is clamped in the liquid conduitgroove 34 by driving, with the use of a punch or the like, the lockingpins 66A into the bores 64A by a distance sufficient to cause theleading ends of the locking pins 66A into interfering engagement withthe sloping, inwardly-facing surfaces 42 of the recesses 40. As in theprevious embodiment, the axes of the bores 64A are at a lesser anglerelative to the bottom wall of the dam body member 50A than the anglebetween the sloping inwardly-facing surfaces 42 and the base of thegroove 34. Accordingly, the clamping pressure exerted on the dam bodymember 50A tending to lock it within the liquid conduit groove 34 issubstantial and progressively increases as the locking pins 66A aredriven further into engagement with the inwardly-facing surfaces 42.

Mold insert bodies have typically been made from a suitable tool steelwith welded-in barriers made from cold rolled steel. Inserts have alsobeen made with aluminum bodies and aluminum barriers. The mold insertbodies 12 of this invention may also be made from tool steels or fromnon-ferrous metals, such as aluminum. However, the entire dam assemblies14 and 14A, including both the body members 50 and 50A and the lockingscrews 66 or pins 66A are preferably made from stainless steel sincestainless steels resist deterioration due to rust or corrosion.

It will be appreciated that in both the first embodiment and in themodification of FIG. 8, a self-contained dam assembly is provided bywhich the dam assembly can be securely clamped within a liquid conduitgroove. A simple tool, such as a screw driver or punch, used to engagethe exposed heads of the locking screws or pins, is all that is neededto effectuate the clamping of the dam assembly in place.

Although this invention is disclosed for use with inserts of the typeshown in said patents, it is apparent that this invention may be usedwith other types of mold inserts, such, for example, as inserts whichare not designed to be used with retainer and lifter assemblies.

This invention can be used to improve the efficiency with which insertscan be inventoried. Because installation is quickly and easilyaccomplished, it is a simple matter to install the dam assemblies 14after the inserts 10 are removed from inventory. Therefore, it isunnecessary to maintain an inventory of inserts 10 which have barriersalready installed or to engage in costly welding operations when insertsare removed from inventory. The dam assemblies 14 can be delivered apartfrom but along with the inserts 10 to a mold making company which couldinstall the dam assemblies 14 at a later time. Also, any person thatuses an insert 10 can easily install additional dam assemblies 14 at anydesired locations within its liquid conduit groove 34.

Although the preferred embodiment of this invention has been described,it will be apparent that various modifications may be made within thepurview of the following claims.

I claim:
 1. In a mold insert for mounting in a master frame of a moldingmachine, said insert comprising a solid metal body having acircumferentially-extending, outwardly-open, liquid conduit grooveformed therein, the improvement wherein said groove has mutuallyconfronting sidewalls each of which is provided with an undercut havingan imperforate, sloping surface facing inwardly of said insert forclamping engagement by one or more locking elements for mounting one ormore liquid barrier dam assemblies in said groove.
 2. The improvement ofclaim 1 wherein said undercuts extend along the entire circumference ofsaid liquid conduit groove.
 3. In a mold insert for mounting in a masterframe of a molding machine, said insert having acircumferentially-extending liquid conduit groove, the improvementwherein said groove has mutually confronting sidewalls each of which isprovided with an undercut having a surface facing inwardly of saidinsert for mounting one or more liquid barrier dam assemblies in saidgroove, and wherein at least one barrier dam assembly is mounted in saidgroove, said barrier dam assembly comprising a body member of a size andshape to fit entirely within said groove, and locking elements locatedentirely within said groove and said body member engaged with saidinwardly-facing surfaces of said undercuts.
 4. The improvement of claim3 wherein said body member and said locking elements are made fromstainless steel.
 5. The improvement of claim 3 wherein said lockingelements comprise screws.
 6. The improvement of claim 3 wherein saidlocking elements comprise locking pins.
 7. The improvement of claim 3wherein said inwardly-facing surfaces slope outwardly of the sidewallsof said groove and inwardly of said insert.
 8. The improvement of claim3 wherein a pair of bores extend through said body member alongrespective axes and open to respective said undercuts, said lockingelements are engaged within said bores and project from said bores intorespective said undercuts, and said respective axes are sufficientlyclose to said inwardly-facing surfaces of said undercuts that portionsof said locking elements bear against said inwardly-facing surfaces ofsaid undercuts.
 9. The improvement of claim 8 wherein saidinwardly-facing surfaces slope outwardly of the sidewalls of said grooveand inwardly of said insert.
 10. In a mold insert for mounting in amaster frame of a molding machine, said insert having acircumferentially-extending liquid conduit groove, the improvementwherein said groove has mutually confronting sidewalls each of which isprovided with an undercut having a surface facing inwardly of saidinsert for mounting one or more liquid barrier dams in said groove; atleast one barrier dam assembly mounted in said groove, said barrier damassembly comprising a body member of a size and shape to fit entirelywithin said groove; and locking means located entirely within saidgroove and said body member engaged with said inwardly-facing surfacesof said undercuts, said locking means comprising a pair of lockingscrews threadedly engaged within tapped bores extending through saidbody member along respective axes which are sufficiently close to saidinwardly-facing surfaces of said undercuts that portions of said lockingscrews bear against said inwardly-facing surfaces of said undercuts. 11.The improvement of claim 10 wherein each of said inwardly-facingsurfaces of said undercuts slopes at an angle “a” relative to the baseof said liquid conduit groove in excess of 45 degrees and wherein eachof said locking screws is held within its said bore at an angle “b”relative to the bottom surface of said dam body member which is lessthan angle “a” so that, as said locking screws are progressivelyadvanced toward said inwardly-facing surfaces, said locking screwsengage said inwardly-facing surfaces with progressively increasingclamping forces.
 12. The improvement of claim 11 wherein said angle “b”is approximately 45 degrees.
 13. The improvement of claim 12 whereinsaid undercuts extend along the entire circumference of said liquidconduit groove.
 14. The improvement of claim 10 wherein saidinwardly-facing surfaces slope a outwardly of the sidewalls of saidgroove and inwardly of said insert.
 15. In a mold insert for mounting ina master frame of a molding machine, said insert having acircumferentially-extending liquid conduit groove, the improvementwherein said groove has mutually confronting sidewalls each of which isprovided with an undercut having a surface facing inwardly of saidinsert for mounting one or more liquid barrier dams in said groove; atleast one barrier dam assembly mounted in said groove, said barrier damassembly comprising a body member of a size and shape to fit entirelywithin said groove; and locking means located entirely within saidgroove and said body member engaged with said inwardly-facing surfacesof said undercuts, said locking means comprising a pair of locking pinsengaged within bores extending through said body member along respectiveaxes which are sufficiently close to said inwardly-facing surfaces ofsaid undercuts that portions of said locking pins bear against saidinwardly-facing surfaces of said undercuts.
 16. The improvement of claim15 wherein each of said inwardly-facing surfaces of said undercutsslopes at an angle “a” relative to the base of said liquid conduitgroove in excess of 45 degrees and wherein each of said locking pins islocated within its said bore at an angle “b” relative to the bottomsurface of said dam body member which is less than angle “a” so that, assaid locking pins are progressively advanced toward said inwardly-facingsurfaces, said locking pins engage said inwardly-facing surfaces withprogressively increasing clamping forces.
 17. The inprovement of claim16 wherein said angle “b” is approximately 45 degrees.
 18. Theimprovement of claim 15 wherein said inwardly-facing surfaces slopeoutwardly of the sidewalls of said groove and inwardly of said insert.